Question

The standard reaction Gibbs energy for a chemical reaction at an absolute temperature T is given by, ${\Delta }_r{G}^o=A-BT$
Where A and B are non-zero constants.
Which of the following is true about this reaction?

• A. Endothermic if, $A<0andB>0$
• B. Exothermic if, $B<0$
• C. Exothermic if $A>0andB<0$
• D. Endothermic if, $A>0$

Answer 1

The correct option is D Endothermic if, $A>0$

According to Gibb's Helmholtz equation,
${\Delta }_r{G}^o={\Delta }_r{H}^o-T{\Delta }_r{S}^o$
Given, ${\Delta }_r{G}^o=A-BT$
On comparing above two equations, we get,
$A=\Delta H^{o}and\Delta S^o=B$
We know that, if $\Delta H^o$ is negative, reaction is exothermic and when it is positive, reaction is endothermic.
$\therefore$ If $A>0$, i.e. positive, reaction is endothermic.